Potassium (K+) is the most abundant intracellular cation, comprising ˜35-40 mEq/kg in humans. See Agarwal, R, et al. (1994) Gastroenterology 107: 548-571; Mandal, A K (1997) Med Clin North Am 81: 611-639. Only 1.5-2.5% of this is extracellular. Potassium is obtained through the diet, mainly through vegetables, fruits, meats and dairy products, with certain food such as potatoes, beans, bananas, beef and turkey being especially rich in this element. See Hunt, C D and Meacham, S L (2001) J Am Diet Assoc 101: 1058-1060; Hazell, T (1985) World Rev Nutr Diet 46: 1-123. In the US, intake is 80 mEq/day. About 80% of this intake is absorbed from the gastrointestinal tract and excreted in the urine, with the balance excreted in sweat and feces. Thus, potassium homeostasis is maintained predominantly through the regulation of renal excretion. Where renal excretion of K+ is impaired, elevated serum K+ levels will occur. Hyperkalemia is a condition wherein serum potassium is greater than about 5.0 mEq/L.
While mild hyperkalemia, defined as serum potassium of about 5.0-6 mEq/L, is not normally life threatening, moderate to severe hyperkalemia (with serum potassium greater than about 6.1 mEq/L) can have grave consequences. Cardiac arrythmias and altered ECG waveforms are diagnostic of hyperkalemia. See Schwartz, M W (1987) Am J Nurs 87: 1292-1299. When serum potassium levels increases above about 9 mEq/L, atrioventricular dissociation, ventricular tachycardia, or ventricular fibrillation can occur.
Hyperkalemia is rare in the general population of healthy individuals. However, certain groups definitely exhibit a higher incidence of hyperkalemia. In patients who are hospitalized, the incidence of hyperkalemia ranges from about 1-10%, depending on the definition of hyperkalemia. Patients at the extremes of life, either premature or elderly, are at high risk. The presence of decreased renal function, genitourinary disease, cancer, severe diabetes, and polypharmacy can also predispose patients to hyperkalemia.
Most of the current treatment options for hyperkalemia are limited to use in hospitals. For example, exchange resins, such as Kayexalate, are not suitable for outpatient or chronic treatment, due to the large doses necessary that leads to very low patient compliance, severe GI side effects and significant introduction of sodium (potentially causing hypernatremia and related fluid retention and hypertension). Diuretics that can remove sodium and potassium from patients via the kidneys are often limited in their efficacy due to underlying kidney disease and frequently related diuretic resistance. Diuretics are also contraindicated in patients where a drop in blood pressure and volume depletion are undesired (e.g. CHF patients that in addition to suffering from low blood pressure are often on a combination of drugs such as ACE inhibitors and potassium sparing diuretics such as spironolactone that can induce hyperkalemia).
The use of cation-binding resins for binding inorganic monovalent cations such as potassium ion and sodium ion has been reported. For example, U.S. Pat. No. 5,718,920 to Notenbomer discloses polymeric core-shell particles said to be effective for binding cations such as sodium ion and potassium ion.
Notwithstanding the progress made in the art, there remains a need for improved compositions for binding inorganic monovalent cations such as potassium ion and sodium ion, and especially, for binding such monovalent cations selectively over divalent cations such as magnesium ion and calcium ion. In particular, there remains a need for improved core-shell particles having a therapeutically effective binding capacity in the physiologically relevant pH range for potassium ion or sodium ion, where such core-shell particles are substantially non-degradable, substantially non-absorbable and are suitable with respect to lack of toxicity. Likewise, there remains a need in the art for improved methods applying such improved compositions, for example in pharmaceutical and other applications involving the removal of monovalent cations from an environment. In particular, there remains a significant need for improved treatment of hyperkalemia, and related indications using such improved compositions.